Conventional thin-film solar cells are manufactured through (1) a front face electrode forming step, (2) a front face electrode patterning step, (3) a photoelectric conversion layer forming step, (4) a photoelectric conversion layer patterning step, (5) a rear face electrode forming step, and (6) a rear face electrode patterning step, for example. Each of the steps will be briefly described below. Note that details of each step is disclosed in JP 2005-259882A, for example, which was already filed by the present applicant, and thus only a simple description thereof is provided here.
(1) Front Face Electrode Forming Step
In the front face electrode forming step, a front face electrode is formed on an insulated light-transmitting substrate such as a glass substrate. Specific examples of the front face electrode include a transparent conductive film formed by using tin oxide, zinc oxide, ITO or the like as a material. In the front face electrode forming step, thermal CVD is favorably used, for example.
(2) Front Face Electrode Patterning Step
By patterning the front face electrode formed in the step (1), a front face electrode separation line is formed. Note that this patterning step includes an alignment step for accurately patterning the front face electrode. In the front face electrode patterning step, patterning utilizing heating by laser irradiation (laser patterning) is favorably used.
(3) Photoelectric Conversion Layer Forming Step
A photoelectric conversion layer is formed on the front face electrode, which has been subjected to patterning in the step (2). As a material for the photoelectric conversion layer, semiconductors made of Si, Ge, SiGe, SiC, SiN, GaAs, SiSn or the like can be used, for example. Also, it is preferable that the semiconductor film of the photoelectric conversion layer has a three-layer structure including p-type, i-type and n-type. In this case, in the photoelectric conversion layer forming step, plasma CVD is favorably used, for example.
(4) Photoelectric Conversion Layer Patterning Step
By patterning the photoelectric conversion layer formed in the step (3), a photoelectric conversion layer separation line is formed. Note that this patterning step includes an alignment step for accurately patterning the photoelectric conversion layer. In the photoelectric conversion layer patterning step, patterning utilizing heating by laser irradiation (laser patterning) is favorably used.
(5) Rear Face Electrode Forming Step
A rear face electrode is formed on the photoelectric conversion layer subjected to patterning in the step (4). Specific examples of the rear face electrode include a laminated film of a transparent conductive film formed by using a material such as tin oxide, zinc oxide, or ITO, and a metal film formed by using a material having good light reflectivity such as Ag, Al or Cr. In particular, a metal film formed by Ag is preferable due to its high reflectance. In this case, in the rear face electrode forming step, the sputtering method is favorably used, for example.
(6) Rear Face Electrode Patterning Step
By patterning the rear face electrode formed in the step (5), a rear face electrode separation line is formed. Note that this patterning step includes an alignment step for accurately patterning the rear face electrode. In the rear face electrode patterning step, patterning utilizing heating by laser irradiation (laser patterning) is favorably used.
Thereafter, a light-transmitting opening portion is formed by irradiating the fundamental wave of YAG laser, for example, from the glass surface onto the rear face electrode that has been subjected to patterning processing. Next, etching is performed in order to remove residues caused by laser processing, and lastly, the rear face electrode side is sealed with an adhesion layer and a transparent sealing material, thereby forming a thin-film solar cell module.
With the above-described manufacturing method, substrates are transported from the front face electrode forming step to the front face electrode patterning step, from the photoelectric conversion layer forming step to the photoelectric conversion layer patterning step, and from the rear face electrode forming step to the rear face electrode patterning step, respectively, by using a transport robot and a substrate cassette.
FIG. 4 illustrates a schematic configuration of a substrate transport system for transporting substrates from the photoelectric conversion layer forming step to the photoelectric conversion layer patterning step, as an example.
In this example, a plasma CVD apparatus 10 is used in the photoelectric conversion layer forming step. Accordingly, this substrate transport system includes the plasma CVD apparatus 10, a first transport robot 20 that retrieves a plurality of substrates (glass substrates) processed by the plasma CVD apparatus 10 one by one, and sequentially stores the substrates in a substrate cassette 30 that is capable of loading substrates in multiple stages, and a second transport robot 40 that retrieves the substrates from the substrate cassette 30 one by one, and transports the substrates to a pre-patterning alignment step 50. Note that a substrate transport system that uses a substrate cassette to transport substrates from a plasma CVD apparatus to the following step is disclosed in Patent Document 1, for example.
The plasma CVD apparatus 10 is a batch-type multiple-stage plasma CVD apparatus capable of loading substrates 1 in multiple stages at predetermined vertical intervals (although five stages are illustrated in this example, the number of stages is not limited to this) and processing the substrates at one time, and is configured by a deposition chamber 11 and a load lock chamber (retrieving chamber) 12.
In the deposition chamber 11 and the load lock chamber 12, as shown in FIG. 5(a), five pairs of supporting pieces 14a and 14b, each horizontally supporting the substrate 1 at the right and left ends thereof, are formed in five stages at predetermined vertical intervals, on side walls 13a and 13b on the right and left sides (the direction perpendicular to the paper in FIG. 4) of each of the chambers 11 and 12, so as to hold the substrates 1 (1a to 1e) respectively in five stages. Also, the substrates 1 are transported from the deposition chamber 11 to the load lock chamber 12 with arms, not shown in the drawings, respectively holding the substrates 1, and moving the substrates 1 from the deposition chamber 11 to the load lock chamber 12 at one time.
On the other hand, the substrate cassette 30 is also configured to be capable of loading the substrates 1 in multiple stages (five stages in this example) at predetermined vertical intervals, as shown in FIG. 5(b). That is, in order to hold the substrates 1 in five stages, five pairs of supporting pieces 33a and 33b, each horizontally supporting the substrate 1 at the right and left ends thereof, are formed in five stages at predetermined vertical intervals, on side walls 32a and 32b on the right and left sides (the direction perpendicular to the paper plane) of a cassette main body 31 so as to hold the substrates 1 in five stages.
The first transport robot 20 holds the substrates 1 with an robot arm one at a time, and transport the substrates 1 from the load lock chamber 12 to the substrate cassette 30. Similarly, the second transport robot 40 also holds the substrates 1 with the robot arm one at a time, and transports the substrates 1 from the substrate cassette 30 to the alignment step.
In the substrate transport system configured as described above, a conventional substrate transport method is performed as follows. Note that when each substrate 1 needs to be distinguished in the following description, a lowercase alphabetical letter is suffixed to the reference numeral 1 representing the substrate in order to distinguish the substrates 1. Also, in principle, in this description, the stages in the load lock chamber 12 and the substrate cassette 30 are counted from the bottom as the first stage, second stage, and the like. A conventional substrate transport method will be described below with reference to FIG. 4.
When five substrates 1a to 1e that have been subjected to the deposition processing are transported from the deposition chamber 11 to the load lock chamber 12, the first transport robot 20 retrieves the substrate 1a in the lowermost stage (the first stage) of the load lock chamber 12, and stores the substrate 1a in the uppermost stage (the fifth stage) of the substrate cassette 30. Next, the first transport robot 20 retrieves the substrate 1b in the second stage of the load lock chamber 12, and stores the substrate 1b in the fourth stage (the second stage from the top) of the substrate cassette 30. Next, the first transport robot 20 retrieves the substrate 1c in the third stage of the load lock chamber 12, and stores the substrate 1c in the third stage (the third stage from the top) of the substrate cassette 30. In this manner, the substrates 1a to 1e are transported from the load lock chamber 12 to the substrate cassette 30 so as to invert the vertical order of the substrates. Accordingly, lastly, the first transport robot 20 retrieves the substrate 1e in the uppermost stage (the fifth stage) of the lock chamber 12, and stores the substrate 1e in the lowermost stage (the first stage) of the substrate cassette 30.
When all the substrates 1a to 1e have been stored in the substrate cassette 30 in this manner, then, the second transport robot 40 first retrieves the substrate 1e in the lowermost stage (the first stage) from the substrate cassette 30, and transports the substrate 1e to the alignment step 50. Next, the second transport robot 40 retrieves the substrate 1d in the second stage of the substrate cassette 30, and transports the substrate 1d to the alignment step 50. Next, the second transport robot 40 retrieves the substrate 1e in the third stage of the substrate cassette 30, and transports the substrate is to the alignment step 50. In this manner, the substrates 1 are sequentially retrieved starting with the lowermost stage, and transported to the alignment step 50. Specifically, the second transport robot 40 lastly retrieves the substrate 1a in the uppermost stage (the fifth stage) of the substrate cassette 30, and transports the substrate 1a to the alignment step 50.